The human neocortex is the part of the brain responsible for language, cognition, social intelligence, thought and goal-directed action. Genetic or environmental influences that alter its development may contribute to, or cause neurodevelopmental disorders, including schizophrenia and autism. This complex structure is comprised of functional units, or areas, that are specifically interconnected. The connectivity, or wiring, of areas contributes to their development and function. In this proposal, I describe experiments that will study the development of neocortical areas by analyzing their connections in normal mice, and in mutant mice that have altered development. I will study intraneocortical connectivity in a mutant that lacks axonal inputs from the thalamus, because of a disruption of thalamic development due to a mutation in the Gbx2 gene. These studies of neocortical development will increase our understanding of basic neurodevelopmental mechanisms, and thereby provide a foundation for elucidating the etiologies that underlie neurodevelopmental disorders. Furthermore, this information may also have relevance to disorders of adulthood, such as schizophrenia, which have been proposed to be due, in part, to abnormalities in brain development.